1. Field of the Invention
This invention pertains in general to switchgear and other switching equipment which use hermetically sealed interrupters employing insulation having a higher electrical resistance than air and more particularly to compact switchgear that employ modular components to reduce the overall size of the system.
2. Background Information
Circuit breakers provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and abnormal level voltage conditions. Typically, circuit breakers include a spring powered operating mechanism which opens electrical contacts to interrupt the current through the conductors on an electrical system in response to abnormal conditions. In particular, vacuum circuit interrupter apparatus have been known which include separable main contacts disposed within an insulating housing. Generally, one of the contacts is fixed relative to both the housing and to an external electrical conductor which is interconnected with the circuit to be controlled by the circuit interrupter. The other contact is moveable. In the case of a vacuum circuit interrupter, the moveable contact assembly usually comprises a stem of circular cross-section having the contact at one end enclosed within a vacuum chamber and a driving mechanism at the other end which is external to the vacuum chamber. An operating rod assembly comprising a push rod, which is fastened to the end of the stem opposite the moveable contact, and a driving mechanism provide the motive force to move the moveable contact into or out of engagement with the fixed contact.
The operating rod assembly is operatively connected to a latchable operating mechanism which is responsive to an abnormal current condition. When an abnormal condition is reached, the latchable operating mechanism becomes unlatched which causes the operating rod to move to the open position. The motion of the operating rod, in turn, causes the contact bell crank to rotate and, as discussed above, this controls motion of the moveable contact.
Compression springs are provided in connection with the operating rod assembly in order to be able to separate the moveable contact from the fixed contact and to assure the necessary force so that the contacts will not accidentally open under inappropriate conditions. In addition, when appropriate circumstances requiring interruption of the circuit do arise, an adequate force is needed to open the contacts with sufficient speed. If the contacts do not open quickly, there is a risk of the contacts welding together and failure to interrupt the current.
Vacuum interrupters or reclosures are typically used, for instance, to reliably interrupt medium voltage ac currents, and in the case of vacuum interrupters also high voltage ac currents of several thousands of amperes or more. Reclosures include interrupters that are designed to typically operate in a range of current measured in amperes, rather than kiloamperes, and automatically reclose after a given delay, and for a given number of times, in an attempt to automatically reestablish the circuit. However, from the standpoint of this invention the principles discussed herein apply equally well to both, as well as to other load break switches, circuit breakers and switch disconnects.
Typically, in accordance with prior art practices, one vacuum interrupter is provided for each phase of a multi-phase circuit and the interrupters for the several phases are actuated simultaneously by a common latchable operating mechanism. This does not permit point-on-wave switching among the multiple phases and can give rise to voltage transient and uneven contact wear.
Medium size switchgear employing vacuum interrupters typically have a front low voltage portion just to the rear of the front panel which typically includes the breaker controls. The low voltage portion is electrically insulated, through the use of standoffs, from high voltage portions which include the vacuum interrupters. The standoffs permit sufficient spacing of the conducting components so that air within the housing can be an effective insulator to isolate the low voltage portions of the switchgear from the high voltage components. However, this spacing also contributes to the size of the units.
More recently attempts have been made to reduce the size of these units by hermetically sealing them and filling them with a gaseous insulator having a higher dielectric capacity than air, such as SF6 However, this creates a number of environmental concerns.
Accordingly, an improved medium voltage switchgear design is desired that reduces the overall size and enhances the serviceability of the unit.
These and other needs are satisfied by the present invention which comprises a circuit switching system made up of a number of plug-in, integral, modular units with each module enclosed within solid electrical insulation that isolates the conducting members that interface between modules, from contact with lower voltage portions of the surroundings. In one embodiment, one of the modules comprises a vacuum switching device (hereafter referred to as the xe2x80x9cisolator modulexe2x80x9d) having a plurality of stationary contacts and a moveable contact mechanism which is connectable to any one of the stationary contacts which are all enclosed in a vacuum vessel, also known as a vacuum bottle. At least two conducting circuit elements are respectively connected to one of the stationary contacts and the moveable contact mechanism with a second stationary contact grounded. The moveable contact within the vacuum vessel of the isolator module is connectable to a contact on a separate breaker module, which can also contain a vacuum circuit interrupter. Each external electrical connection on the isolator module which is connectable to either a line source, e.g., main bus bar, or an electrical connector on the separate breaker module, terminates in an insulated electrical connector that is designed to mate with a complementary insulated electrical connector on the line source, and the breaker module. The other external electrical connections on the switching system modules that interface with either other modules in the system or the circuit interface, also, similarly employ complementary insulated electrical connectors, electrically insulating the interface from the external environment and sealing those mating electrical connectors from contact with lower voltage portions of the surroundings, while maintaining a good electrical connection; with the possible exception of a ground connection. If only a single line source is used when the isolator module is designed to accommodate more than one, the exposed electrical connector is fitted with a fully insulated, complementary connector, in the form of a complementary non-electrically conducting plug, to isolate the unused electrical connector from lower voltage portions of the surrounding switching system or environment, e.g., air. The vacuum isolator module is operable to connect the breaker module alternatively to one or more sources or ground in the event servicing is required or, with both contacts in the open state the isolator module can isolate the breaker module in a floating condition.
The breaker module forms a second modular component of this invention that includes a conventional vacuum interrupter, designed to withstand the currents experienced by the breaker function, whose terminals are connected to insulated electrical connectors that protrude through the vacuum vessel. Desirably both breaker module insulated electrical connectors protruding through the vacuum bottle are of the same design so that either can be connected to either side of the circuit. The breaker module further includes an integral, or separate, in-line actuator which is dedicated to actuating the moveable contact on the breaker module and is preferably enclosed within an insulated housing that could encompass both the vacuum vessel and the in-line actuator. In a preferred embodiment the in-line actuator employs two coils, each respectively controlling a different direction of movement of the moveable contact. The voltage on each of the in-line actuator coils can be controlled independently so that the moveable contact can be appropriately energized to move in the desired direction and braked to ease the moveable contact to a soft landing. Alternatively, a single coil can be employed with a means for reversing current through the coil. A single vacuum isolator module and breaker module, comprising a vacuum interrupter and in-line actuator, is employed for each phase of the circuit.
A load connector forms a third module of this invention. The load connector module includes separate insulated electrical output connectors for each phase of the load, which are designed to mate with complementary insulated electrical connectors on the load interface, electrically insulating the interface from the external environment and sealing those mating connectors from lower voltage portions of the surroundings, while maintaining a good electrical connection. The load connector module also includes integral current monitoring transformers for each phase, and an electrical connection to plug in a modular voltage transformer. The load connector module further includes insulated electrical input connectors, which are respectively in electrical contact with the corresponding output electrical connectors, and respectively mate with a complementary electrical connector on each of the breaker modules. The load connector module components are housed in a solid, electrically insulated housing.
A point-on wave-controller module is also provided which in one embodiment is adapted to receive inputs from the three-phase current monitoring transformers, the voltage transformer and sensors monitoring the position, speed, temperature and past history of the breaker module components and the control voltage available. The point-on-wave controller analyzes characteristics of the breaker module and the load current wave form, monitors and receives inputs from the circuit trip relays and provides directions to the in-line actuators to open or close the appropriate phases at appropriate times to minimize voltage transients and adverse impact to the circuit and circuit switching system components. The point-on-wave controller is particularly useful in minimizing arcing upon closing of the circuit by closing each phase at its current zero and reduce the probability of reignition.
Accordingly, the current carrying components of the modular units are fully insulated from lower voltage portions of the surrounding, employing separable complementary, insulated, electrical connectors. In addition, the outside layer of each modular unit""s housing is covered with an electrically conductive coating which permits the modules to be in close contact without ionizing the surrounding air. The prescribed insulation and electrically conductive coating that enable the various modules to be positioned much closer together within the circuit switching system housing, thus significantly reducing the overall size of the switching system housing. The separable, detachable modules further enhance servicing while the point-on-wave controller and breaking capability of the in-line actuators extend the useful life of the integral components and those of the system.